In light of increasingly higher viscosity indexes and lower viscosities of lubricant oils in recent years, research is being conducted toward high-viscosity index base oils that have not been obtainable except synthetic oils in the prior art. Driving system oils are considered to require base oils of lower viscosity than engine oils, to maintain the low viscosity at low temperature demanded for device design from the viewpoint of energy savings, and high-viscosity index base oils are being sought in order to further increase energy efficiency.
Improvement in the low-temperature characteristics is usually achieved by adding a pour point depressant or the like to the lubricating base oil (see Patent documents 1-3, for example). Known methods for producing high-viscosity index base oils include processes in which feedstock oils containing natural or synthetic normal paraffins are subjected to lubricating base oil refining by hydrocracking/hydroisomerization (see Patent document 4, for example).
On the other hand, when devices are designed with smaller sizes and higher performance for automobile fuel efficiency, the lubricant oil is exposed to even higher temperature, and problems occur such as oil volume reduction due to oil evaporation and lubricant oil viscosity increase due to light component evaporation. It has therefore been attempted to lower the evaporation properties of lubricant oils (see Patent documents 5-7, for example).
Furthermore, in light of increased requirements for safety in recent years, and storage-related issues, a demand exists for high flash point base oils, and petroleum products that are a rank higher than ordinary petroleum products, and research is being conducted toward their realization (see Patent document 8, for example).    [Patent document 1] Japanese Unexamined Patent Application Publication HEI No. 4-3 63 91    [Patent document 2] Japanese Unexamined Patent Application Publication HEI No. 4-68082    [Patent document 3] Japanese Unexamined Patent Application Publication HEI No. 4-120193    [Patent document 4] Japanese Patent Public Inspection No. 2006-502298    [Patent document 5] Japanese Unexamined Patent Application Publication HEI No. 10-183154    [Patent document 6] Japanese Unexamined Patent Application Publication No. 2001-089779    [Patent document 7] Japanese Patent Public Inspection No. 2006-502303    [Patent document 8] Japanese Unexamined Patent Application Publication No. 2005-154760